The valve lock screws are the 2 screws on the side of the gun that hold the valve in place. They go through the receiver body, through the power tube, and screw directly in to the valve body.

Sold individually or in kits.

Uh Oh! If these holes are stripped out, it is the valve body that must be replaced. Your power tube and receiver should still be fine. You can get the valve body by itself (hard to assemble and re-assemble) or complete with the internal pieces (suggested). Do not play with just 1 screw in place. The marker might stutter and break paint. You are more likely then to crack your power tube and cause other problems.